Anecdotal reports of malaria infecfions in South Asia indicate that the classical symptoms of P. falciparum and P. vivax malaria are rapidly changing. Malaria parasite populafions that have the capacity to rapidly alter their genetic makeup, to avoid drugs or to avoid host immune responses, may contribute to this change in pathogenesis. Since all of the aspects that contribute to the pathogenesis of malaria infecfion cannot be addressed in a single project, we have chosen to focus on host mechanisms that remove infected erythrocytes from peripheral circulafion and the parasites'ability to sequester in specific fissues in order to avoid the spleen. Project 3 is divided into two specific aims for understanding malaria pathogenesis. The first aim will study cytoadhesion and acquired immunity during pregnancy associated malaria, particulariy in the context of varying genetic plasticity. The second aim will indirectly measure splenic function by observing deformability of cells in peripheral circulafion and correlating this with the clinical severity of malaria infection. The P. falciparum erythrocyte membrane 1 (PfEMPI) proteins, encoded by the var gene family, play a key role in parasite cytoadherance and evading host clearance of infected erythrocytes. The best understood paradigm of pathogenesis is pregnancy associated malaria. This syndrome is a major cause of poor mother/child health and is associated with placental sequestrafion of P. falciparum infected erythrocytes (lEs) by a single PfEMPI variant. We will study acquired immunity to pregnancy malaria, the antigenic diversity of adhesion blocking epitopes in East and West India, and the evolution of polymorphism in parasite populafions that differ in mutagenic potential by the ARMD phenotype. The Rathod lab has developed a microfiuidic assay to indirecfiy observe splenic filtrafion by observing the minimum cylindrical diameter of erythrocytes in peripheral circulation. The minimum cylindrical diameter (MCD) is a parameter which describes the smallest sized tube which an erythrocyte may successfully pass through without lysing or becoming trapped. The MCD is particulariy useful for describing the probability of a cell becoming trapped as it passes through a filter. If the spleen is essenfially a filter for erythrocytes in peripheral circulation, then splenic filtration is thought to define the MCD profile of cells in circulation. Data from a preliminary study in Malawi indicates that MCD profiles vary between individuals and may correlate with severity of malaria infecfion. This project will use microfiuidic devices to indirecfiy observe splenic filtration by the MCD profile of individuals and the presentation of malaria infection